The present invention relates to an improved process for the preparation of high fructose corn syrup, particularly, to an improved process for converting glucose to high fructose corn syrup using enzyme isomerization techniques.
Heretofore, corn and other vegetable starches have been converted to glucose using a strong acid such as hydrochloric acid or enzymes which catalyze the breakdown of the starch to glucose. Since the converted starches are not sufficiently sweet to compete with sucrose in many applications, a microorganism capable of producing glucose isomerase which converts glucose to the sweeter fructose has been employed. The resulting corn syrup is commonly referred to as high fructose corn syrup or simply HFCS. Methods for producing HFCS, including the often employed enrichment and polishing operations, are well-known in the art.
In conventional methods for preparing HFCS, the glucose which has been produced from the corn and/or other vegetable starch using conventional techniques is deashed and decolorized prior to actual enzyme isomerization of the glucose to a glucose/fructose mixture. Conventionally, deashing (specifically the removal of sulfate and chloride salts of calcium, magnesium and potassium) and decolorizing is achieved by sequentially treating the glucose with a strong acid, cation-exchange resin and subsequently with a weak base, anion-exchange resin. The strong acid, cation-exchange resin removes the cationic species, e.g., calcium, magnesium and potassium cations from the glucosic process stream. Alternatively, the weak base, anion-exchange resin removes the chloride and sulfate anions from the process stream. In addition, the anion-exchange resin removes significant amounts of the color bodies originally present in the corn syrup.
Subsequent to the treatment with the ion-exchange resins, the pH of the corn syrup is generally from about 8 to 10. Since an acidic pH of from about 4 to 6 is required for effective enzyme isomerization of the glucose to fructose, an acid such as HCl is added to the glucosic syrup.
The glucose is then isomerized. The resulting glucose/fructose mixture is purified by sequentially treating the mixture with a strong acid, cation-exchange resin and a strong base, anion-exchange resin and subsequently recovered using conventional techniques.
Unfortunately, in the described process, the adjustment of the pH of the glucosic syrup by adding the strong acid prior to the enzyme isomerization step introduces undesirable anionic impurities in the process stream which must be removed subsequently during the purification of the glucose/fructose mixture. In addition, the amino acids and amino acid derivatives, which acids and derivatives are commonly found in the glucosic process stream, are generally the first ionic components to leak from strong acid resin and undesirably high amounts of the acids and their derivatives are often present during the actual isomerization step.
Moreover, upon the exhaustion of the anion resin employed in the deashing/decolorization operations (i.e., the reduction in the ability of the resin to remove anions from the glucosic syrup to a commercially impractical level), the resin must subsequently be regenerated prior to its reuse. In conventional processes, the anion resin is regenerated using either a sodium carbonate, ammonium hydroxide or sodium hydroxide solution. Unfortunately, following regeneration, the resin must be thoroughly rinsed using deionized water to remove the desired amounts of sodium, ammonium and compounds thereof entrapped or otherwise entrained within the anion resin during regeneration. After multiple cycles of operation (e.g., 100 operation cycles), undesirable large amounts of rinse water, for example up to 20 to 30 resin bed volumes are required to rinse the desired amounts of sodium from the resins. Although the ammonium cations are more easily rinsed from the regenerated resin, ammonium hydroxide possesses a noxious odor and does not effectively remove trapped organic bodies from the anion-exchange resin during regeneration.
In view of the aforementioned deficiencies of the prior art in preparing HFCS, it remains highly desirable to provide an improved method for producing HFCS which does not have the aforementioned deficiencies.